System for transposition of conductor sets in cables



H. NYQUIST Aug. 15, 1933.

SYSTEM FOR TRANSPOSITION OF CONDUCTOR SETS IN CABLES Filed D90. 1931 A N Car/Aer Carrier Gil-acuity JWor/nal non- INVENTOR EJV wt BY ATTORNEY Patented Aug. 15, 1933 SYSTEM FOR TRANsiosrrIoN bn, CON- DUCTOR sETsuNoAn ns 1 Harry Nyquist, Millburn; assignor t o American Telephone and TelegraphCo'rnpany, a Corporation of-New York Application December 17,1531

I Serial No.:581,742

9 Claims: (01. 179-78) It is among the objects of my invention to provide a new and improved system of transposition of conductors in a cable system. Another object of my invention is to provide for the operation of twin cables, one of them for transmission one way at its ends and the other. for transmission the opposite way at its ends with transpositionsoi the conductor pairs systematically disposed-at certain points between the ends. Another object of my invention is to arrange a corresponding system of transpositions in a single cable with a shield. All these objects and other objects and advantages of my invention will become apparent on ,consideration'.of. a limited number of examples of practice according to the invention which I have chosen fordis clo sure in this specification. It will be understood that the follow, ing disclosurefreilates principally, to these particular examples'of the inventioniand that; its scope will be indicated in the appended claims.

Referring to the drawing,- Figure l is a diagrammatic representation of an embodiment of my invention in twin cables; Fig. 2'is a detail to which reference will be made in explaining the principles involved in Fig. '1; and Fig. 3 is a diagram showing my invention embodied in a single cable with a shield within it.

. Referring to Fig. 1, thisrepresents two cables extending between stations C and A respectively east and west. Each linerepresents a conductor pair. The pairs a and c are combined in a fourwire system with terminal a at the left, and similarly, the pairs b and d are combined in a four-wire system with its terminal b at the left. The triangular symbols R in Fig. 1 represent repeaters with their points directed toward the output ends. The circle symbols T are usual threewinding transformers, and the, square symbols N are usual balancing networks} It will be seen that all the pairs have repeaters at station A at the leftand that those pairs which enter cable I at this place have repeaters with their outputs entering the cable, but the pairs in cable 11 at the left have repeaters with their input ends toward the cable II. It will also be seen that at the opposite end at the station C there are similar repeaters similarly directed. But at intermediate stations certain of the conductor pairs are transposed.

The conductor pairs a, c and b, d that have just been identified, belonging to four-wire systems, are Worked at voice frequencies. In addi tion there are conductor pairs in the same cable such as e and I that are worked at higher frequencies, that is, at carrier current f equencies. Such pairs require intermediate repeaters at the intermediate ,stationB in addition to therepeaters at the end stations A'a-nd. C, but the voicefrequencypairs do not require ,such intermediate repeaters. 1 1 I the high-frequency pair such as e and the low-frequency pair such as a and, b were disposed at station- B, as indicated in Fig. 2, then on the output side of the-repeaterthere .would be energy at high level whichyvould cause nearend crossatalk-into a neighboring conductor or conductors of apair such-as; -a. .This near-end cross-talk inthe conductor or conductors of, pair a would get, around byzanother stage of near-end cross-talk-to the inputside of therepeaterin pair 6 and so there would be circulation of energy with. amplification .ateach cycle. To guard against this the other pairs such as a are transposed from one cable to the other. Accordingly, although=the firsts tage of cross-talk mentioned in. connection with Fig. 2 may occur in Fig. l, the second stage cannot occur'because of such transposition. I

Having transposedall thepairs such as a at station.B, each suchpairv is transposed back again at a junction place wherethere are no repeaterssuch as A or C. In this way the ends of thestretch, as shown in Fig.- 1 at A and C,,appear as distincttwin cables, all the inputs being into one -.c able at one end and all the outputs being from the same cable ,at the oppositeend, and vice versa. i

In an ordinary. twin'cable system, worked on the four-wire plan, if onewcable is interrupted as by an accident, it'renders theother. cable entirely useless for two-way conversation purposes. -But .according to the system of transpositions .here employed, if there is an interruption of one cable at any point between A .and C along its length, half of the voice frequency four-wire circuits will remain uninterrupted, thus, for example, if the lower cable in Fig. 1 is interrupted between the points A -.and B. nevertheless the four-wire system with. terminal a' at the left, remains intact. Similarly,-itcan be seenthat if a section of either cable in either stage A to B or B to C is interrupted, only one of the two-four-wire systems with terminals a and b at the left, will be put out of service.

To makethe probability of damage as small as possible, the four-wire voice circuits should be grouped as shown in Fig; 1 and at the same time the points A and C should be located as far apart as possible in the total stretch A to C. The minimum distance that will be permisthe outer compartment and so that each repeater receives its input from an inner compartment."

In this way, with the transpositions shown, the

inner compartment is generallyoperated at a lower power level than the outer compartment. The low frequency or voice frequency lines have repeaters only at A and C, but the carrier cur rent lines at high frequency have additional re-' peaters at the intermediate point B and these are also disposed so that the high power level parts of the lines near the repeater-outputs are in the outercompartment. Thus inductive interterence acting on the cable will involve principally those parts of the lines that are athigh power level and will therefore be relatively insignificant and, on the other hand, the parts of the linesat low power level will generally be withinthe inner compartment and will there fore be especially shielded from interference. The principle is followed throughout that wherever there is a one-way repeater, the low level circuit connected to the input of that repeater is in thelow level compartment, that is the inner compartment, and the high level circuit connected to the output of that repeater is in the high level compartment, that is the outer compartment. This requires an odd number of transpositions between the main repeater offices such as A and C. These oflices are fifty miles apart, and the carrier lines have additional repeaters at B, which willtherefore be twentyfive miles apart, and additional transposition points must be provided at A'cnd'C so that transpositions can be made at twelve and onehalf mile intervals.

In the case of two-wire circuits, of course there is no particular point which can be designated as a high level point in contrast to another point as a low level point and, consequently, there is no particular advantage in transposing these circuits between the inner and outer compartments. There would be no harm in transposing them as for the circuits involved in four-wire systems provided that the transposition is not made at a point where there are carrier repeaters only. Such circuits may'be considered as exceptional non-carrier circuits and may be connected-simply as shown by the dotted lines in Fig. 3. There is a particular reason for keeping ascertaincircuit in the same compartment for a considerable distance in the case where such circuit is connected to an open wire line which may bring in considerable interference, particularly longitudinal disturbances. When such a circuit is kept in the high-level compartment from the point of entry in the cable to the first repeater oflice it will do a minimum amount of harm.

I claim:

..L A cable conductor system comprising two shielded compartments side by side, conductor pairs therein, and repeaters for certain of said pairs at a certain point along the length of said cable conductor system, the conductor pairs having such repeaters being transposed at this point relatively to the pairs not having such repeaters at this point.

2. A cable conductor system comprising two shielded compartments side by side, conductor pairstherein, repeaters at the ends of said compartments, three transposition places along the compartments between the ends, and repeaters for certain of said pairs at the middle transposition point, the pairs having the repeaters at this point being relatively transposed as compared with the pairs not having the repeaters at this same point. 3, .A twin cable conductor system comprising two :cables extending side by side between two places, certain of the conductor pairs being transposed systemmatically from one cable to the other and back so that if one cable is interrupted, only half of the four-wire circuits will be put out of service.

wire high frequency service, repeaters in all these pairs at certain points and additional repeaters in the high frequency pairs at additional inter- ..iediate points, the pairs being transposed at said last .entioned repeaters so that any low frequency conductor in the same compartment with a high frequency conductor on the input side of the repeater will be in a different compartment on the output side of the same repeater.

6. A cable conductor system having an interior shield, a plurality of conductor pairs in said cable, repeaters associated with said pairs, the parts of the conductors connected to the repeater outputs being in the outer compartments of the cable and the parts of the conductors connected to the repeater inputs being in the inner compartment of the cable, the conductors being transposed to effeet the foregoing arrangement.

'7. A multi-conductor cable of a certain length having low frequency and high frequency pairs therein, and having an interior shield, repeaters for all these pairs at the ends of this length of cable, additional repeaters interposed in the high frequency pairs at an intermediate point of the length of the cable, the interior shield being interrupted at the place of the last mentioned repeaters and at two other places between the middle and the ends of the length of cable, and the pairs being transposed between the outer compartment and the inner compartment so that all the repeaters shall deliver their outputs directly to the outer compartment and receive their inputs directly from the inner compartment.

8. The method of disposing conductors in a two compartment cable system with repeaters, which consists in connecting all repeater inputs to conductors in one compartment and all repeater outputs to conductors in the other compartment and transposing to effect this arrangement.

9. In a multi-conductor cable system, the meth- 0d of preventing feed-back at a repeater through a conductor set not repeatered at that point which consists in transposing the conductors in and out of said repeater relatively to said set.

HARRY NYQUIST. 

